High-pressure superalloy turbine blades, or turbine vanes, of gas turbine engines utilise a combination of internal cooling, external cooling and a ceramic thermal barrier coating (TBC) in order to lower the temperature of the substrate temperature of the superalloy turbine blades, or turbine vanes, to allow them to operate effectively within the high-pressure turbine of the gas turbine engine with minimal degradation. Ceramic thermal barrier coatings are deposited by plasma spraying or by electron beam physical vapour deposition (EBPVD).
In order to maintain adhesion of an electron beam physical vapour deposited (EBPVD) ceramic thermal barrier coating (TBC) for the life of the turbine blade, or turbine vane, a bond coating which forms a dense adherent and slow-growing oxide, e.g. alumina, bonding layer is required as an intermediate layer between the superalloy substrate of the turbine blade, or turbine vane, and the ceramic thermal barrier coating.
The bond coatings are generally either overlay coatings, e.g. MCrAlY bond coatings where M is one or more of nickel, cobalt and iron, Cr is chromium, Al is aluminium and Y is one or more of yttrium, ytterbium, lanthanum and other rare earth metals, or aluminide bond coatings. The aluminide bond coatings may for example comprise a simple aluminide bond coating, a chromium aluminide bond coating, a platinum aluminide bond coating or a chromium platinum aluminide bond coating. MCrAlY coating are generally deposited by thermal spraying or electron beam physical vapour deposition and aluminide coatings are generally deposited by chemical vapour deposition, e.g. pack aluminising, out of pack aluminising, slurry aluminising, etc.
A further bond coating comprises a platinum enriched surface layer on the superalloy substrate comprising platinum enriched gamma phase and platinum enriched gamma prime phase. Another bond coating comprises an overlay, e.g. MCrAlY, coating, a platinum enriched outer overlay layer and a platinum aluminide layer on the platinum enriched overlay layer. The platinum is generally deposited by electroplating and is diffusion heat treated.
Conventionally, the surface of the bond coating is prepared before the ceramic thermal barrier coating is applied by electron beam physical vapour deposition (EBPVD) to improve the adhesion of the ceramic thermal barrier coating to the bond coating and hence increase the working life of the ceramic thermal barrier coating. The surface of the bond coating is made smooth, by polishing or grit blasting, so that a uniform adherent oxide, e.g. alumina, bonding layer is formed.
The present disclosure seeks to provide a novel thermal barrier coated superalloy article which has an improved working life.
The present invention seeks to provide a novel method of applying a thermal barrier coating to a superalloy article to produce a thermal barrier coated article which has an improved working life.